This invention relates generally to the fields of biochemistry and molecular medicine, and more specifically to polypeptide substrates for matrix metalloproteinases.
Proteinases are a class of enzymes that are involved in the cleavage or hydrolysis of a variety of proteins. Matrix metalloproteinases (MMPs) are a family of structurally related proteinases that have been implicated in the hydrolysis of several proteins, including proteins involved in blood vessel formation (angiogenesis) and proteins that make up the extracellular matrix (ECM). These proteinases are mediators of both normal and pathological processes in the body. For example, matrix metalloproteinases are involved in normal tissue remodeling, such as wound healing, and normal angiogenesis, such as occurs in the female reproductive cycle. However, these proteinases are also involved in pathological processes such as angiogenesis within tumors and tumor metastasis.
Several matrix metalloproteinases have been implicated in tumor invasion. For example, membrane type-I matrix metalloproteinase (MT1-MMP) is expressed in various tumors. This metalloproteinase is known to hydrolyze many types of ECM proteins such as interstitial collagens, gelatin and proteoglycan. In addition, MT1-MMP is an activator of another matrix metalloproteinase, MMP-2. MMP-2 (also called gelatinase A) is also expressed in various tumors and, when activated, can play a role in metastatic processes. When MMP-2 activity is reduced, as seen in genetically engineered mice that lack the MMP-2 gene, tumor angiogenesis is also reduced. A third matrix metalloproteinase of interest in tumorigensis is MMP-9 (also called gelatinase B). This metalloproteinase is reported to be part of the “angiogenic switch” that initiates the vascularization of tumors. Solid tumors require vascularization for growth and so this matrix metalloproteinase, as well as other matrix metalloproteinases, has been a target for designing drugs to inhibit matrix metalloproteinase function and tumor angiogenesis. However, many of these drugs are broad spectrum metalloproteinase inhibitors and exhibit unwanted side effects.
Since matrix metalloproteinases are overexpressed at sites of disease they represent an opportunity for designing new therapeutic and diagnostic agents. In the case of therapeutic agents, there is a need for methods of targeting biologically active compounds to the site of MMP action. Such targeting can increase the efficacy of these compounds while reducing their unwanted side effects. Several groups have put forth strategies in which a compound can be targeted to a desired site of action by linking it to a binding molecule that binds selectively at a desired site. However, binding molecules with sufficient affinity and selectivity are not always available, particularly for the MMPs. The present invention overcomes this problem by providing polypeptides that are selective MMP substrates. In the case of diagnostic agents, there is a need to be able to measure MMP activity, both in vitro and in vivo. Most current approaches measure MMP expression level; however, because the MMPs are regulated post-translationally, protein expression levels do not indicate protease activity. The present invention provides selective MMP substrate polypeptides that are cleaved by catalytically active MMPs and so these polypeptides can be used to quantify MMP activity for diagnostic uses.
Thus, there exists a need to identify selective substrates that can target a specific active matrix metalloproteinase for use as diagnostics and therapeutics. The present invention satisfies this need and provides related advantages as well.